Field of the Invention
The present invention generally relates to wireless communication networks. More particularly, the present invention relates to an advanced receiver architecture applicable in wireless communication networks based on OFDM (“Orthogonal Frequency Division Multiplexing”) and MIMO (“Multiple Input Multiple Output”) techniques—such as LTE (“Long Term Evolution”), LTE-Advanced and WiMax (“Worldwide Interoperability for Microwave Access”) networks.
Overview of the Related Art
Evolution of wireless communications has experimented a significant growth in terms of spread and performance, and has recently brought to 3GPP LTE (“Third Generation Partnership Project Long Term Evolution”)/LTE-Advanced and WiMax standards.
Such standards are conceived for allowing high-speed transmissions.
In order to achieve that, a combination of OFDM and MIMO techniques is used for transmission. According to OFDM technique, bits to be transmitted are split into bits sequences, then the bits sequences are modulated by separate and reciprocally orthogonal sub-carriers and multiplexed into a data stream (i.e., a stream of data including (OFDM) symbols, or symbols stream) for transmission. According to MIMO technique, multiple symbols streams are transmitted/received via multiple transmitting/receiving antennas.
However, the growing number of mobile network users, as well as the growing demand for services requiring very high data traffic (such as internet, multimedia and real-time services) and the evolution of mobile applications have brought to higher and higher user data rates requirements.
In order to fulfill such requirements, optimization and upgrade of wireless networks could be an insufficient, inefficient and/or unaffordable approach.
Another approach is to devise, at the user terminal side, algorithms aimed at increasing throughput, and receiver architectures adapted to implement them.
Receiver architectures available in literature substantially show two peculiar design choices, namely non-iterative receivers and iterative receivers.
In non-iterative receivers, de-multiplexing is performed by means of algorithms that approximate ML (“Maximum Likelihood”) detection, such as QRD-M, Sphere decoding, or SOMA (“Soft-Output M-Algorithm”) algorithms. Such algorithms, and especially the QRD-M algorithm, allow obtaining performance close to ML detection, but with lower complexity.
In iterative receivers, iterative processing is performed for inter-stream interference cancellation (such as “Successive Interference Cancellation”, SIC, or “Parallel Interference Cancellation”, PIC) and noise enhancement reduction. In iterative receivers, de-multiplexing is performed by means of MMSE (“Minimum Mean Square Error”), ZF (“Zero Forcing”) or V-BLAST algorithms.
In the state of the art, different solutions based on, or having reference to, non-iterative and iterative receivers are known.
WO2008/027554 discloses a method and apparatus for QR decomposition-based MIMO detection and soft bit generation. QR decomposition is performed on MIMO channel matrix H to compute a Q matrix and an R matrix such that H=QR. The R matrix, or diagonal elements of the R matrix, is stored in a memory. By using a matrix computed by dividing elements in each row of the R matrix by a corresponding diagonal element of the R matrix, and a vector computed by dividing each element of the received symbol vector by a corresponding diagonal element of the R matrix, a tree search process is performed to generate an approximate maximum likelihood (ML) estimate of transmitted symbols.
US2010/0271988 discloses a method and system for MIMO detection and channel decoding. The method comprises decomposing a channel complex gain matrix into a unitary matrix and an upper right hand triangular matrix; providing a received signal to a complex conjugate transpose of the unitary matrix, thereby creating a plurality of signals; normalizing a last of the plurality of signals; channel decoding the normalized last of the plurality of signals, thereby recovering a last codeword signal; encoding the last codeword signal; utilizing the encoded last codeword signal to recover a second last codeword signal; and repeating the utilizing until all codeword signals are recovered. Also, a method and system for providing an imbalanced modulation and coding scheme for successive interference cancellation is disclosed.
WO2008/069467 discloses an iterative receiver comprising a signal detector for estimating interference from an estimated transmitted signal and canceling the estimated interference from a signal received through an antenna; a decoder for performing channel decoding by using the interference cancelled received signal; a soft decision unit for performing a soft decision process on the transmitted signal by using the channel decoded signal; a channel estimator for estimating a channel by using the soft decision applied transmitted signal and the received signal; a covariance estimator for estimating covariance on the sum signal of the interference and noise by using the soft decision applied transmitted signal, the received signal, and the estimated channel; and a hard decision unit for determining the transmitted signal by using the channel decoded signal after interference cancellation, channel decoding, estimated transmitted signal updating, channel estimation, and covariance estimation are iterated a number of times.
WO 2010/031005 discloses a receiver comprising an inner decoder that includes a linear front-end followed by a limited tree-search based on a soft-output M-algorithm, a conventional near-optimal or optimal decoder for the outer binary code, and iterative decoding (ID), whereby decoding (output) information is passed from one decoder module as input to the other and used to refine and improve the inner/outer decoding module outputs.